Soon throughout much of the country, shoppers will be able to buy clothes, footwear, school supplies, and (sometimes) computers, sports equipment, or almost anything their hearts desire—and pay no sales tax. So why not just wait a few days to get your back-to-school shopping done?

At least 16 states are hosting tax-free shopping events in the near future, including 11 states waiving sales tax on many purchases this weekend: Alabama, Arkansas, Iowa, Louisiana, Missouri, New Mexico, North Carolina, Oklahoma, South Carolina, Tennessee, and Virginia. Other states—Connecticut, Florida, Maryland, Massachusetts, Texas—hold their tax-free weekends later in August.

Over the last few years, tax-free shopping days have become a traditional means of boosting back-to-school sales for retailers. But, given the dire situations in many states’ budgets, however, it’s not surprising that the events—which cost the states significant tax revenues—aren’t slam dunks for approval by legislators.

Each state’s tax holiday is a little different. Louisiana’s, for instance, is one of the most comprehensive, in which the usual 4% sales tax is waived on almost all purchases up to $2,500. Iowa, on the other hand, is only waiving sales tax this weekend on purchases of clothing—footwear is OK, but not jewelry or watches—selling for $100 or less. The state even stipulates rules for retailers and consumers creatively attempting to get around the $100 maximum. For example:

A suit is normally priced at $125.00 on a single price tag. The suit cannot be split into separate articles so that any of the items may be sold for under $100.00 in order to qualify for the exemption.

The sales tax holiday in Missouri is more or less typical, with purchases of up to $50 of school supplies, $100 of clothing, and $3,500 of computer equipment available with no sales tax from Friday-Sunday this weekend. But it’s noteworthy that dozens of Missouri cities that have opted out of the event will be charging sales tax like usual.

By now, you should be getting the impression that these sales tax holidays come with plenty of exceptions and fine print. Before heading to the register with all sorts of items you’d assumed to be buying with no sales tax, take a close look at the rules in the state where you’re shopping by following the links here.